When Fabian Cancellara won a flat stage (not TT) he did something that does not happen all that often. In fact one way or the other he will have a record of sorts. Assuming he does not win the Tour this will be the latest a Yellow Jersey wearer won a flat stage and did not win the Tour. If he does win (somehow) it will be the earliest in a Tour that a winner has done this. (Actually it turns out that winning a flat stage in yellow has only been done once between stages 4 and 15 inclusive, guess who).
If Rasmussen does end up in Yellow and Polkadot (yes a longshot) he will be the first since Merckx to do so and the first since Hinault to pick up 2 jerseys in one Tour.
Anyone else notice any other rare events or reasonable possibilities?
NOTE: Actually everything is limited to since ww II, mainly because the site I found that has stage winner and yellow in a nice layout only goes back that far. But that does cover a lot, remember the early days had no Yellow Jersey.